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A 45 year old female comes to the ER with an abscess on her thigh. After a full assessment and evaluation, you recognize a large abscess on her thigh, which should amenable to I&D. However, the patient states that she has a lidocaine allergy. She is adamant that she had a severe reaction during a dental procedure ten years ago and says she does not want any local anesthesia at all with anything that has “-caine” in it’s name because her dentist told her to avoid all of these. She never had an sensitivity testing or allergic testing to determine what class of anesthetic she was allergic to. What could be an alternative for local anesthesia for this patient if she refuses any general sedation?

True allergies to “-caines” are very rare, estimated at about 1-2% of all adverse reactions. However, they can be potentially serious. Ester solutions have a higher incidence of reactions than compared to amides. Many times, it is the preservative that the patient is allergic and this component may the reason for a reaction to both amides and esters. However, there is a very low true cross reactivity between the amide and ester themselves. The metabolite paraaminobenzoic acid is usually the culprit causing the reaction the patient attributes their anesthetic allergy to. The problem facing us in the ER however is that a lot of these patients do not remember what exact type of local anesthetic they received and many of the reactions could be due to adverse drug affects of things such as epinephrine in combination preparations of these anesthetics. Due to the uncertainty that surrounds these presumed allergies, alternatives may be required to avoid sedations for some straightforward procedures which could be successfully accomplished using other injectable local agents. Diphenhydramine (DPH) has been utilized in a wide variety of settings as a local anesthetic as an alternative to local anesthetics. (1,2) Studies have shown efficacy in the usage of solutions of up to 1% of DPH as a local anesthetic. In these studies, DPH has shown comparable anesthesia during suture repairs when compared to lidocaine, although the initial injection of DPH was perceived to be more painful by the patients. (3) There was an isolated incidence of skin necrosis in a single patient in this series. There have also been other studies showing the efficacy of a lower concentration of DPH at 0.5% showing efficacy as an alternative to local anesthetic. However this study showed a decreased efficacy of the drug at this concentration when used on the face. (4) An excellent review and summary of the literature has shown that experiences with DPH as an anesthetic resulted in anesthesia for 15 minutes to three hours. Side effects of this alternative include sedation, local skin irritation and patchy anesthesia and tingling when used as a digital block. Thus digital blocks are not recommended with DPH. Other relative contraindications include pregnancy, asthma, PUD, narrow angle glaucoma, BPH, and bowel obstruction (5,6). 1. Green SM, Rothrock SG, Gorchynski J. Validation of diphenhydramine as a dermal local anesthetic. Ann Emerg Med. 1994;23(6):1284–1289. [PubMed] 2. Bartfield JM, Jandreau SW, Raccio-Robak N. Randomized trial of diphenhydramine versus benzyl alcohol with epinephrine as an alternative to lidocaine local anesthesia. Ann Emerg Med. 1998;32(6):650–654. [PubMed] 3. Ernst AA, Anand P, Nick T, Wassmuth S. Lidocaine versus diphenhydramine for anesthesia in the repair of minor lacerations. J Trauma. 1993;34(3):354–357. [PubMed] 4. Ernst AA, Marvez-Valls E, Mall G, et al. 1% lidocaine versus 0.5% diphenhydramine for local anesthesia in minor laceration repair. Ann Emerg Med. 1994;23(6):1328–1332. [PubMed] 5. Gallo WJ, Ellis E., 3 Efficacy of diphenhydramine hydrochloride for local anesthesia before oral surgery. J Am Dent Assoc. 1987;115(2):263–266. [PubMed] 6. Pavlidake PG, et. al. Diphenhydramine as an Alternative Local Anesthetic Agent. The Journal of Clinical and Aesthetic Dermatology. Oct 2009. 7. Roberts and Hedges’ Clinical Procedures in Emergency Medicine. 6th Edition. Chapter 29: Local and Topical Anesthesia.

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